Implement fast_normalize builtin v4

This implementation was ported from the AMD builtin library
and has been tested with piglit, OpenCV, and the ocl conformance tests.

v2:
  - Remove f suffix from constant in double implementations.
  - Consolidate implementations using the .cl/.inc approach.

v3:
 - Use __CLC_FPSIZE instead of __CLC_FP{32,64}

v4 (Jan Vesely):
 - Limit to single precision.

llvm-svn: 236920